Apparatus for applying and drying chromatographic samples

ABSTRACT

A portable sampling apparatus with intermittent drying action and drying only a defined area of the test surface, having a frame provided with a slot marked with evenly spaced indicia and through which liquid chemical substances or samples may be applied to a surface for chromatographic and other purposes. Air, nitrogen, or any other suitable, known gas is normally directed uniformly through a manifold arranged surrounding the slot and onto the surface for drying the sample. A plate is pivotally mounted on the frame for functioning as a hand rest for an operator applying the sample to a surface, and a projection on the plate is arranged for being biased against a resilient tube forming a part of a fluid flow passage supplying the manifold for blocking the flow passage while a sample is being applied to the surface.

United States Patent 1191 Martinez [11] 3,857,784 1451 Dec. 31, 1974APPARATUS FOR APPLYING AND DRYING Primary Examiner-John AdeeCHROMATOGRAPHIC SAMPLES Attorney, Agent, or Firm-Norbert P. Holler; BertJ. [75] Inventor: Sylvia Martinez, Coral Gables, Fla. Lewen [73]Assignee: SINDCO, Coral Gables, Fla. [57] ABSTRACT 22 i Oct 27 1972 Aportable sampling apparatus with intermittent drying action and dryingonly a defined area of the test [21] Appl 301583 surface, having a frameprovided with a slot marked with evenly spaced indicia and through whichliquid 52 us. Cl 210/198 chemical substances 91 Samples y be pp to a[51] Int. Cl B01d 15/08 Surface for chromatographic and other P p Air,[58] Field of Search 210/31 0, 198; 117/106 A, nitrogen, or y othersuitable, known gas is normally 117 1193; 113 3 directed uniformlythrough a manifold arranged surrounding the slot and onto the surfacefor drying the [56] References Cit d sample. A plate is pivotallymounted on the frame for UNITED STATES PATENTS functioning as a handrest for an operator applying the sample to a surface, and a projectionon the plate is gzg gg et a1 2% arranged for being biased against aresilient tube form- 3229505 1/1964 Sanford e i iii i1:11....11l. 210/310 mg a of a mud flow Passage Supplying the fold for blocking the flowpassage while a sample is being applied to the surface.

11 Claims, 4 Drawing Figures 3/8 so 50 52 I6 22 I2 I 2e 4 APPARATUS FORAPPLYING AND DRYING CHROMATOGRAPHIC SAMPLES BACKGROUND OF THE INVENTIONl. Field of the Invention This invention relates generally to samplingapparatus, and in particular to such apparatus used for chrmatographicand other suitable purposes.

2. Description of the Prior Art Chromatography may be defined as aseparating of compounds in a solution or mixture by seeping the solutionor mixture through an adsorbent. Each compound in the solution ormixture will become adsorbed in a separate, frequently colored layer.This procedure has numerous applications in chemical analysis, andseveral forms of chromatographic analysis are employed in the chemicalarts. Among these forms are paper, thin-layer, and vapor phasechromatography.

In the performance of these chromatographic processes, it is usuallynecessary to subject a sample to a drying medium immediately upon thedeposition of the sample on a sample-receiving or test surface. Arelatively complex apparatus is known which automatically appliessamples to a test surface in the form of streaks or spots. This knowndevice has a bore arranged beneath the test surface for directing a flowof air thereto for penetrating through the material forming the testsurface and drying the samples. However, since the air must pass throughthe surface forming material, this known device is restricted for use inperforming paper chromatography where paper and other porous materialsare employed, and is not suitable for use in thinlayer chromatographywhich employs glass, metal, plastic, and other impermeable materials.Further, this known device cannot be used when it is necessary toprovide a flow of a gas other than air as for preventing the sample fromoxidizing or to cause the sample to react with a particular gas for aspecified purpose.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a time saving, efficiency increasing, simple and reliableapparatus for simultaneously applying and drying liquid chemical sampleson various surfaces for chromatographic and other purposes, protectingthe sample in the applicator means from being evaporated.

It is another object of the present invention to provide a samplingapparatus with which samples may be protected against oxidation, orpurposely oxidized or reacted with an appropriate gas for a specifiedpurpose.

These and other objects are achieved according to the present inventionby providing an apparatus for drying samples of a fluid substance whichhas an arrangement for directing a flow of a drying medium onto a testsurface for drying a sample of a fluid substance on the surface, and anarrangement for interrupting the drying medium flow when a sample isbeing applied to the surface.

In general, the apparatus includes a base structure adapted to besupported on a table top or the like and providing a defined area whichis accessible from above and within the confines of which asample-receiving portion of the test surface may be located. The basestructure further provides a conduit system for directing a flow ofadrying gas from an intake section of the system to a discharge sectionat the test surface location, and means are provided for establishingcommunication between a source of drying gas under pressure and theintake section of the conduit system and for regulating the flow ofdrying gas into the conduit system and for regulating the flow of dryinggas into the conduit system. The latter includes, intermediate theintake and discharge sections thereof, an open-shut valve arrangementactuatable from above, and a manually displaceable operating memberhaving a valveengaging adjunct thereon is hinged to the base structurein overlying relation to the valve arrangement, so that only when anoperator rests his hand on the operating member and depresses the same,the valve arrangement is closed. In this manner, the flow of drying gascan be interrupted by the operator resting on the operating member thehand in which he is holding the liquid applicator, so that during theapplication of each sample to the test surface, drying of the liquidsubstance in the applicator device is prevented, while drying of thesamples can then, simply by the lifting of the operators hand, becommenced immediately after the application of the sample to the testsurface.

A preferred embodiment of an apparatus according to the presentinvention has a frame provided with an opening in the form of a slot fordefining an area in which a sample is applied to a test surface. Thisframe includes a pair of members arranged for cooperating when placedtogether to form the slot and the drying medium flow directingarrangement. The directing arrangement advantageously has a manifoldsurrounding the slot, and grooves provided in one of the members. Apiece of resilient tubing is arranged in an opening provided in themember having the grooves so as to form a portion of a flow passagebetween the fluid source and the manifold. The interrupting arrangementhas a projection which is arranged for selectively engaging the tubingand blocking the flow passage.

Preferably, the tube blocking projection is provided on a platepivotally mounted to the frame and arranged for engagement by a hand ofan operator applying a sample to the sample surface for biasing theprojection against the tubing and blocking the flow passage while thesample is being applied.

The member not provided with the fluid passage grooves advantageouslyhas a planar portion in which a portion of the slot and the tubingreceiving opening are arranged, and depending side wall portionsextending transversely with respect to the planar surface for supportingthe apparatus on a suitable supporting member such as a table top.Recesses are formed in the side wall portions for receiving an articlesuch as a pipette, glass rod, and the like for separating a film forminga test surface from the supporting member. This will prevent seepagewhen using a porous material such as a paper or other materialconstructed from a glass fiber or other porous material as the film.

Samples may be applied and dried to a test surface according to themethod of the present invention by directing a flow of drying mediumdirectly onto a receiving test surface for drying a sample of a fluidsubstance on the surface, applying selectively a sample to the testsurface as by an operator resting a hand on the pivotally mounted plateand wetting the test surface with a fluid substance from a pipette andthe like, and inter rupting the drying medium flow when a sample isbeing applied as by the pressure of the hand on the pivotally mountedplate blocking the resilient tubing forming part of the flow passage.Thus the drying action is stopped while the sample is being spotted onthe test surface and reinitiated when the sampling means is raised.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part thereof, whereinlike numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, perspectiveview showing a sample applying and drying apparatus according to thepresent invention.

FIG. 2 is an exploded, perspective view showing the apparatus of FIG. 1.

FIG. 3 is a fragmentary, sectional view taken generally along the line3-3 of FIG. 1.

FIG. 4 is a fragmentary, sectional view showing a detail of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularlyto the drawings, there is shown an apparatus according to the presentinvention for applying and drying samples of a fluid substance such as asolution or mixture. This apparatus 10 has a conduit system orarrangement 12 (FIG. 3) for directing a flow of a drying medium onto atest surface 14 for drying a sample 16 (FIG. 3) of a fluid substancedeposited on surface 14in a manner to be discussed below. Apparatus 10also has an arrangement 18 for interrupting the drying medium flow whena sample 16 is being applied to the surface 14.

Apparatus 10 is shown as having a frame or base structure 20 providedwith an opening in the form of a slot 22 for defining an area in which asample 16 is applied to surface 14. Frame 20 includes a pair of members24 and 26 arranged for cooperating when placed together to form slot 22and the conduit system or arrangement 12. Member 24 may be referred toas an upper plate, and member 26 as a lower plate. Arrangement 12includes a manifold 28 surrounding slot 22 and formed as by spacedprojections 29 extending from the bottom of a recess in member 26, andgrooves 30 (FIG. 2) also provided in member 26.

Arrangement 12 also includes an open-shut valve constituted, in theillustrated embodiment of the invention, of a section of tubing 32constructed from a resilient material such as a synthetic rubber andforming a flow passage in cooperation with grooves 30. Arrangement 18 isprovided with a projection 34 arranged for selectively engaging tubing32 and blocking its flow passage. An opening 36 is provided in member 24for receiving tubing 32. Selective blocking of the passage way of tubing32 is achieved by a cover plate or operating member 38 pivotally mountedon member 24 of the base structure as by conventional hinges 40.Projection 34 is mounted on the surface of plate 38 adjacent member 24.Plate 38 is arranged for engagement by a hand (not shown) of an operatorapplying a sample 16 as by a pipette and the like to surface 14 forbiasing projection 34 against tubing 32 and blocking the flow passage oftubing 32 while a sample 16 is being applied. Tubing 32 is mounted tomembers 24, 26 as by a pair of fittings 42 formed from two parts 44 and46. Part 44 is illustrated as integral with member 24, and part 46 asintegral with member 26. When the plates or members 24, 26 are arrangedabutting one another, parts 44 and 46 will cooperate to form fittings42. Tubing 32 may he slipped over fittings 42 in a conventional mannerand be retained thereon as by the pointed, annular gripping members.Portions of plate or member 26 are removed to permit tubing 32 to fitover fitting parts 46. A web 48 is left between these cut out portionsto provide an abutment surface cooperating with projection 34 to blockthe passageway of tubing 32. The intake section of the conduit system,at the end of grooves 30 most distant from the discharge section ormanifold 28, is adapted to be attached to a suitable, known gas flowregulating valve 50. This valve 50 may in turn be connected to a hoseleading from a suitable, known source of an appropriate gas underpressure. Member 24 has a planar portion 52in which opening 36 and itsportion of slot 22 are arranged, and depending side wall portions 54extending transversely with respect to planar portion 52 for supportingthe apparatus on a suitable supporting member 56. Member 56 may be atable top and the like. Side wall portions 54 have formed thereinrecesses 58 for receiving an article 60 such as a pipette, glass rod,and the like for separating a film 62 forming test surface 14 fromsupporting member 56 when film 62 is, for example, a paper constructedfrom glass fiber or some other porous material. This will preventseepage of the liquid sample through the porous material and onto thesupporting member 56. This separation is not necessary when a thin layersheet having glass, metal, plastic, and the like backing is used.

It is to be understood that although any suitable, known valve 50 may beemployed with an apparatus 10 according to the present invention. valve50 forms part of the invention and is selectively connectible to a hose(not shown) for connection to an appropriate source of pressurized gas.The numbering illustrated in FIGS. 1 and 2 between slot 22 and the edgeof member 24 is only exemplary, and it is to be understood that otherappropriate markings may be used if desired. The markings withoutindicia on the other longitudinal side of slot 22 are advantageouslyplaced in an alternate manner to the first-mentioned markings.

Plate members 24 and 26 may be assembled in a suitable, known manner, asby gluing with a suitable, known adhesive. Further, article 60 should beselected of a diameter sufficient small as to allow for ample spacebetween it and plate or member 26. This is so a chromatographic testsurface such as film 62 can be placed between article 60 and member 26in such a manner that film 62 does not press against the adjacentsurface of member 26, but only just touches it.

In operation, a chromatographic-surface such as film 62 is placed underapparatus 10 in such a way that a sample application line on film 62 isarranged at the center of slot 22. Air or any other appropriate gas isallowed to enter apparatus 10 through valve 50, which may be adjusted toregulate the gas flow. Liquid sample drops are deposited through theaperture formed by slot 22 and onto the surface 14 of film 62 in asequential manner in such a way that when the small volume of liquiddrop is deposited on surface 14 by means of a micropipette or any othersimilar supporting device (not shown), the weight ofa hand on plate 38stops the gas flow. Removal of the hand from plate 38 restores the gasflow. Once the gas flow is restored, the spotted sample 16 isimmediately evaporated or dried in a uniform manner so that dispersionof the area occupied by sample 16 on surface 14 is either reduced to aminimum or completely eliminated. This sequence is continued until allthe appropriate samples have been spotted.

Manifold 28 is designed specifically to provide a uniform flow of gasthrough all and each one of its plurality of openings and into slot 22.In this manner, all samples are dried at the same rate. Thechannels-that is, the recess and the grooves 30-in member 26 are shownexaggerated for clarity. In actuality, they would be, for example, 15 tothousandths of an inch deep.

An apparatus 10, which may be referred to as a sampler or sampleapplicator, according to the present invention is advantageouslyconstructed from materials resistant to most chemicals and solvents.This may be achieved as by, for example, molding members 24, 26 fromappropriate synthetic resin. Recesses 58, which are preferably in theform of semi-circles, allow the use of articles 60 which are commonlyand conveniently found in chemical laboratories. The markings andindicia on the edge of slot 22 allow even spacing with identification ofsamples according to a predetermined number. Any lightweight surfacecommonly used for chromatography or any other similar purpose is helddown in place by apparatus 10 not is now blown by the gas flow, anoccurrence common with conventional, known dryers of this type.

An apparatus 10 according to the present invention is designed toprovide an even flow of gas throughout the entire aperture of slot 22,thus allowing a fast, even drying or evaporation of an applied liquidsample drop. Suitable hot gases may be used to accelerate theevaporation of the sample, and suitable inert gases, such as nitrogenand the like, may be used for protection of unstable samples. Reactivegases may be used to produce chemical changes on the applied sample, insitu. The gas flow may be actuated at will while the liquid sample isbeing applied merely by lifting the hand from plate 38. Since there isusually no gas flow while the liquid sample is being applied, there ispractically no evaporation of the sample in the micropipette or othersampling device being used. This evaporation is practically unavoidablewhen using conventional dryers and can be of critical importance whenrunning quantitative runs with volatile solvents. Since the evaporationor drying of the sample is obtained so easily and uniformly, theapplication of a sample can be made in smaller amounts, producingsmaller spot areas which give better definition and separation.

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed, and accordingly all suitable modifications and equivalentsmay be resorted to, falling within the scope of the invention.

. What is claimed as new is as follows:

1. A simple, portable, manually actuatable apparatus for use in theapplication to a chromatographic test surface, and in the drying on thetest surface, of one or more samples ofa liquid substance to be driedand analyzed, comprising, in combination:

a. a base structure adapted to be supported on a table top or the likeand providing i. a defined area within the confines of which asample-receiving portion of the test surface may be located, and

ii. a conduit system for directing a flow of a drying gas from an intakesection of said conduit system to a discharge section thereof at saiddefined area and there to each location of a sample on the test surface,said conduit system including an openshut valve means intermediate saidintake and discharge sections and positioned for actuation fromexteriorly of said base structure;

b. means for establishing communication between said intake section ofsaid conduit system and a source of drying gas under pressure andincluding means for regulating the flow of drying gas into said conduitsystem; and

c. a manually displaceable operating member hingedly connected to saidbase structure, said operating member having an adjunct arranged tooperate said valve means'so as to close the latter when said operatingmember is engaged and pressed toward said base structure by the hand ofan operator;

d. whereby the flow of drying gas to said defined area can first beinterrupted by the hand of the operator while a sample is being appliedto the test surface and can then be renewed simply by the lifting of theoperators hand, so that i. drying of the portion of the liquid substancewhich remains in the applicator device during the application of eachsample to the test surface is prevented, and

ii. drying of the sample can nevertheless be commenced immediately afterthe application thereof to the test surface.

2. A simple, portable, manually actuatable apparatus for use in theapplication to a chromatographic test surface, and in the drying on thetest surface, of one or more samples of a liquid substance to be driedand analyzed, comprising, in combination:

a. a base structure adapted to be supported on a table top or the likeand providing i. a defined area which is accessible from above andwithin the confines of which a sample-receiving portion of the testsurface may be located, and

ii. a conduit system for directing a flow of a drying gas from an intakesection of said conduit system to a discharge section thereof at saiddefined area and there to each location of a sample on the test surface,said conduit system including an openshut valve means intermediate saidintake and discharge sections and positioned for actuation from above;

b. means for establishing communication between said intake section ofsaid conduit system and a source of drying gas under pressure andincluding means for regulating the flow of drying gas into said conduitsystem; and

c. a manually displaceable operating member overlying the top of saidbase structure and hingedly connected thereto, said operating memberhaving an adjunct arranged to operate said valve means so as to closethe latter when said operating member is engaged from above and presseddown toward said base structureby the hand of an operator holding anapplicator device;

(1. whereby the flow of drying gas to said defined area can first beinterrupted by the hand of the operator while a sample is being appliedto the test surface and can then be renewed simply by the lifting of anoperators hand, so that i. drying of the portion of the liquid substancewhich remains in the applicator device during the application of eachsample to the test surface is prevented, and

ii. drying of the sample can nevertheless be commenced immediately afterthe application thereof to the test surface.

3. An apparatus according to claim 2, wherein said base structurecomprises a horizontal plate member provided with a slot-shaped openingwhich constitutes said defined area and beneath which saidsamplereceivirig portion of the test surface may be located.

4. An apparatus according to claim 3, wherein said conduit system atsaid discharge section thereof includes a manifold providing a pluralityof outlet apertures for admitting drying gas into said slot-shapedopening at a corresponding plurality of locations.

5. An apparatus according to claim 2, wherein said open-shut valve meanscomprises a length of resilient, flexible tubing supported on said basestructure and defining an interior passageway which is a part of saidconduit system, and said operating member is mounted so as to have saidadjunct thereof engage and compress said tubing for closing saidpassageway when said operating member is pressed toward said basestructure.

6. An apparatus according to claim 2, wherein said base structurecomprises first and second horizontal plate members located one atop theother, each of said plate members being provided with a respectiveslotshaped aperture, said apertures being vertically aligned with oneanother and together forming a slot-shaped opening which constitutessaid defined area and beneath which said sample-receiving portion of thetest surface may be located, and said plate members at their abuttingsurfaces being cooperatively constructed to define said conduit systemwith said discharge section thereof in communication with saidslot-shaped open- 8 ing.

7. An apparatus according toclaim 6, wherein the upper one of said platemembers has a second opening therein located above an imperforateportion ofa lower one of said plate members, said plate memberscooperatively define a pair of fittings extending into said secondopening, said open-shut valve means comprises a length of resilient,flexible tubing overlying said imperforate portion of said lower platemember and connected at its opposite ends to said fittings and defininga normally open interior passageway which is a part of said conduitsystem, and said operating member is mounted so as to have said adjunctthereof engage and compress said tubing against said imperforate portionof said lower plate member for closing said passageway when saidoperating member is pressed sufficiently far down toward said upperplate member.

8. An apparatus according to claim 7, wherein said operating member is athird plate member hinged at one edge to one of said upper and lowerplate members and having on its surface directed toward said upper platemember a projection constituting said adjunct and adapted to enter saidsecond opening for engagement with said tubing.

9. An apparatus according to claim 8, wherein said third plate member ishinged on said upper plate memher at a location remote from saidslot-shaped opening.

10. An apparatus according to claim 9, wherein said upper plate memberhas a pair of downwardly depending opposed side walls, said lower platemember fits into the space between said side walls, and said side wallsare provided with respective recesses aligned with one another below thelevel of the bottom surface of said lower plate member to define a spacefor insertion of an elongated member therethrough adapted to underlieand support a test surface element beneath said slot-shaped opening.

11. An apparatus according to claim 10, wherein said upper plate memberhas markings alongside said slotshaped opening to designate locationsfor the application of plural samples to the test surface.

* l l I

1. A simple, portable, manually actuatable apparatus for use in theapplication to a chromatographic test surface, and in the drying on thetest surface, of one or more samples of a liquid substance to be driedand analyzed, comprising, in combination: a. a base structure adapted tobe supported on a table top or the like and providing i. a defined areawithin the confines of which a samplereceiving portion of the testsurface may be located, and ii. a conduit system for directing a flow ofa drying gas from an intake section of said conduit system to adischarge section thereof at said defined area and there to eachlocation of a sample on the test surface, said conduit system includingan open-shut valve means intermediate said intake and discharge sectionsand positioned for actuation from exteriorly of said base structure; b.means for establishing communication between said intake section of saidconduit system and a source of drying gas under pressure and includingmeans for regulating the flow of drying gas into said conduit system;and c. a manually displaceable operating member hingedly connected tosaid base structure, said operating member having an adjunct arranged tooperate said valve means so as to close the latter when said operatingmember is engaged and pressed toward said base structure by the hand ofan operator; d. whereby the flow of drying gas to said defined area canfirst be interrupted by the hand of the operator while a sample is beingapplied to the test surface and can then be renewed simply by thelifting of the operator''s hand, so that i. drying of the portion of theliquid substance which remains in the applicator device during theapplication of each sample to the test surface is prevented, and ii.drying of the sample can nevertheless be commenced immediately after theapplication thereof to the test surface.
 2. A simple, portable, manuallyactuatable apparatus for use in the application to a chromatographictest surface, and in the drying On the test surface, of one or moresamples of a liquid substance to be dried and analyzed, comprising, incombination: a. a base structure adapted to be supported on a table topor the like and providing i. a defined area which is accessible fromabove and within the confines of which a sample-receiving portion of thetest surface may be located, and ii. a conduit system for directing aflow of a drying gas from an intake section of said conduit system to adischarge section thereof at said defined area and there to eachlocation of a sample on the test surface, said conduit system includingan open-shut valve means intermediate said intake and discharge sectionsand positioned for actuation from above; b. means for establishingcommunication between said intake section of said conduit system and asource of drying gas under pressure and including means for regulatingthe flow of drying gas into said conduit system; and c. a manuallydisplaceable operating member overlying the top of said base structureand hingedly connected thereto, said operating member having an adjunctarranged to operate said valve means so as to close the latter when saidoperating member is engaged from above and pressed down toward said basestructure by the hand of an operator holding an applicator device; d.whereby the flow of drying gas to said defined area can first beinterrupted by the hand of the operator while a sample is being appliedto the test surface and can then be renewed simply by the lifting of anoperator''s hand, so that i. drying of the portion of the liquidsubstance which remains in the applicator device during the applicationof each sample to the test surface is prevented, and ii. drying of thesample can nevertheless be commenced immediately after the applicationthereof to the test surface.
 3. An apparatus according to claim 2,wherein said base structure comprises a horizontal plate member providedwith a slot-shaped opening which constitutes said defined area andbeneath which said sample-receiving portion of the test surface may belocated.
 4. An apparatus according to claim 3, wherein said conduitsystem at said discharge section thereof includes a manifold providing aplurality of outlet apertures for admitting drying gas into saidslot-shaped opening at a corresponding plurality of locations.
 5. Anapparatus according to claim 2, wherein said open-shut valve meanscomprises a length of resilient, flexible tubing supported on said basestructure and defining an interior passageway which is a part of saidconduit system, and said operating member is mounted so as to have saidadjunct thereof engage and compress said tubing for closing saidpassageway when said operating member is pressed toward said basestructure.
 6. An apparatus according to claim 2, wherein said basestructure comprises first and second horizontal plate members locatedone atop the other, each of said plate members being provided with arespective slot-shaped aperture, said apertures being vertically alignedwith one another and together forming a slot-shaped opening whichconstitutes said defined area and beneath which said sample-receivingportion of the test surface may be located, and said plate members attheir abutting surfaces being cooperatively constructed to define saidconduit system with said discharge section thereof in communication withsaid slot-shaped opening.
 7. An apparatus according to claim 6, whereinthe upper one of said plate members has a second opening therein locatedabove an imperforate portion of a lower one of said plate members, saidplate members cooperatively define a pair of fittings extending intosaid second opening, said open-shut valve means comprises a length ofresilient, flexible tubing overlying said imperforate portion of saidlower plate member and connected at its opposite ends to said fittingsand defining a normally open interior passageway which is a part of saidconduit system, and said operatinG member is mounted so as to have saidadjunct thereof engage and compress said tubing against said imperforateportion of said lower plate member for closing said passageway when saidoperating member is pressed sufficiently far down toward said upperplate member.
 8. An apparatus according to claim 7, wherein saidoperating member is a third plate member hinged at one edge to one ofsaid upper and lower plate members and having on its surface directedtoward said upper plate member a projection constituting said adjunctand adapted to enter said second opening for engagement with saidtubing.
 9. An apparatus according to claim 8, wherein said third platemember is hinged on said upper plate member at a location remote fromsaid slot-shaped opening.
 10. An apparatus according to claim 9, whereinsaid upper plate member has a pair of downwardly depending opposed sidewalls, said lower plate member fits into the space between said sidewalls, and said side walls are provided with respective recesses alignedwith one another below the level of the bottom surface of said lowerplate member to define a space for insertion of an elongated membertherethrough adapted to underlie and support a test surface elementbeneath said slot-shaped opening.
 11. An apparatus according to claim10, wherein said upper plate member has markings alongside saidslot-shaped opening to designate locations for the application of pluralsamples to the test surface.